Exemplary embodiments relate to a radio-frequency (RF) signal receiver used for a wireless communication, and more particularly, relate to a dual band receiver capable of making direct frequency down-conversion and receiving simultaneously two signals transmitted via different frequency bands.
In addition to a small-sized RF communication system, a need for a next-generation RF communication receiver with the flexibility, adaptability, and cognitivity is being increased. Such a need may be satisfied by placing an Analog-to-Digital Converter (ADC) to be closer to an antenna and making frequency conversion and demodulation using a Digital Signal Processor (DSP). A next-generation RF communication receiver satisfying such a condition may be a band pass sampling receiver. The band pass sampling receiver may provide excellent functionality in relation to reconfiguration and multi-band/multi-mode receiving.
A typical band pass sampling receiver may receive an analog RF signal via an antenna and the received signal is bandpass-filtered through an analog bandpass filter. The bandpass-filtered analog signal may be amplified via a Low Noise Amplifier (LNA) and converted into a digital baseband signal via an Analog-Digital Converter ADC. Since the bandpass sampling receiver does not require an analog device such as a mixer and a local oscillator, it may provide a flexible, low cost, and small wireless communication receiver. However, the typical band pass sampling receiver may receive a single RF signal. Further, the typical bandpass sampling receiver may down-convert a received analog RF signal into a baseband signal of a digital format only when a carrier frequency is integer times of a sample rate in receiving a single RF signal.
To simultaneously receive two signals at any frequency band using a general band pass sampling receiver, a sampling rate must be determined such that interference between two signals is not generated at a baseband after digital conversion. However, it is very difficult to determine a sampling rate such that interference between two signals is not generated. Further, a solution of the sampling rate making interference between two signals not generated can't be often obtained. Accordingly, there is limited to simultaneously receive two RF signals at any frequency band using the general band pass sampling receiver.
There may increase a need for a dual band (or, multi-band) receiver which receives simultaneously at least two or more different frequency band signals or at least two or more different communications standards signals, via a single receiver. Further, a communication technique such as a cognitive radio communications system may require a function of receiving any frequency band signal and at the same time, scanning whether a signal exists at another frequency band. However, a general dual band receiver may have a receiver circuit or chip every mode, frequency band, or channel. Accordingly, a receiver may become complicated and expensive. As a result, there is required a receiver which supports a dual band and a dual mode using a single receiver circuit.